Electrolysis can purify copper by using an electrochemical cell where impure copper dissolves and pure copper is deposited.
The Electrolytic Process
The process utilizes the principles of electrolysis, where an electric current drives the transfer of metal ions in a solution. Here's a breakdown:
- Electrodes:
- Anode (Positive Electrode): The impure copper is used as the anode.
- Cathode (Negative Electrode): A strip of pure copper serves as the cathode.
- Electrolyte: An aqueous solution containing copper(II) ions, such as copper(II) sulfate (CuSO₄), is used as the electrolyte.
- Process: When an electric current is applied:
- At the Anode: Copper atoms from the impure copper anode lose electrons (oxidation) and dissolve into the electrolyte as copper ions (Cu²⁺). The reference states, "When the electric current is switched on, copper ions are dissolved at the anode...". Other metallic impurities at the anode may also dissolve, depending on their electrochemical properties.
- At the Cathode: Copper ions (Cu²⁺) from the electrolyte migrate towards the cathode. At the cathode, these copper ions gain electrons (reduction) and are deposited as pure copper atoms, increasing the mass of the pure copper cathode. The reference states, "...migrate towards the cathode and are deposited as pure copper".
- Impurities: Impurities present in the impure copper anode behave differently:
- More Reactive Metals: More reactive metals (those more easily oxidized than copper) also dissolve into the electrolyte as ions. However, under appropriate voltage conditions, only copper ions are reduced at the cathode.
- Less Reactive Metals: Less reactive metals (those less easily oxidized than copper) do not dissolve. Instead, they form an "anode sludge" or "anode mud" at the bottom of the electrolytic cell. This sludge can contain valuable metals like gold and silver, which can be recovered as byproducts.
Diagram of Copper Purification by Electrolysis
| Component | Description |
|---|---|
| Anode | Impure copper electrode where oxidation occurs. |
| Cathode | Pure copper electrode where reduction occurs. |
| Electrolyte | Copper(II) sulfate solution, providing Cu²⁺ ions. |
| Power Supply | Provides the electric current to drive the electrolytic process. |
| Anode Sludge | Residue containing less reactive metals that do not dissolve. |
| Overall Process | Impure copper dissolves, and pure copper is deposited, separating impurities. |
Advantages of Electrolytic Purification
- High purity copper is obtained (typically >99.99% purity).
- Valuable byproducts (e.g., gold, silver) can be recovered from the anode sludge.
